This invention generally relates to a gas turbine engine, and more particularly to a method for influencing a variable contour of a nacelle assembly during abnormal aircraft operating conditions.
In an aircraft gas turbine engine, such as a turbofan engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. The hot combustion gases flow downstream through turbine stages which extract energy from the hot combustion gases. A fan supplies air to the compressor.
Combustion gases are discharged from the turbofan engine through a core exhaust nozzle and a quantity of fan air is discharged through an annular fan exhaust nozzle defined at least partially by a nacelle assembly surrounding the core engine. A majority of propulsion thrust is provided by the pressurized fan air which is discharged through the fan exhaust nozzle, while the remaining thrust is provided by the combustion gases discharged through the core exhaust nozzle.
It is known in the field of aircraft gas turbine engines that the performance of the turbofan engine varies during diversified operability conditions experienced by the aircraft. An inlet lip section located at the foremost end of the turbofan nacelle assembly is typically designed to enable operation of the turbofan engine and reduce separation of airflow from the inner and outer flow surfaces of the inlet lip section during these diversified conditions. For example, the inlet lip section requires a “thick” inlet lip section to support operation of the engine during specific flight conditions, such as crosswind conditions, takeoff conditions and the like. Disadvantageously, the “thick” inlet lip section may reduce the efficiency of the turbofan engine during normal cruise conditions of the aircraft, for example. As a result, the maximum diameter of the nacelle assembly is approximately ten to twenty percent larger than required during cruise conditions.
An aircraft may also experience a variety of abnormal aircraft operating conditions, including but not limited to, windmilling engine-out conditions and fan blade-out conditions. Disadvantageously, the performance characteristics of the gas turbine engine may drastically decrease during abnormal aircraft operating conditions of this type. Known nacelle assemblies have not fully reduced the drag penalties, flow separation and pressure recovery problems that occur during the abnormal aircraft operating conditions.
Accordingly, it is desirable to improve the performance of a turbofan gas turbine engine during abnormal aircraft operating conditions to provide a nacelle assembly having a reduced thickness, reduced weight and reduced drag.